Weather Blog

A journey through the inversion

A journey through the inversion
Former UW grad and now Portland-area meteorologist Justin Sharp took his family snowshoeing and sledding in the Mt. Hood area on Sunday.  He sent to me his meteorological diary of his trip, which does a fantastic job of highlighting the variability of the weather around here recently with the strong temperature inversion. 

Here's what he found:

"1) Gusty winds as I left home in east Portland.  Temperature 44 F.

2) Wind gusts well over 40 knots in the Gresham area with sustained winds elevating traffic lights at a 45 degree angle.  Temperature 42 F. 
Looking east at Mt Hood from I-84, the mountain appeared out of focus in the mid-elevations.  I'm fairly certain that the density continuity was so sharp that it was creating a significant optical effect.

3) Wind dies along the road to Sandy, temperature 42 to 44. 4) Coming into the city of Sandy (elev ~1000ft), gust winds, temperature rises from 44 to 49 through the length of the town (about 1.5 miles and maybe a few hundred feet of elevation gain).  Sandy is a relative high spot in the pass that HWY 26 goes along.

5) Temperature drops back down to 42 F continuing down Hwy 26.

6) Proceeding into the immediate lee of the Cascades at Zigzag (2000 ft) which is surrounded by high terrain the temperature drops down to 31 F as the area is within its own local drainage pool

7) Heading up towards Govt Camp the temperature climbs to a maximum of 48F at about 3400 ft.  The warm spot is accompanied by locally strong winds - probably downslope in the immediate lee of the pass.

8) At Ski Bowl in Govt Camp (~3900 ft+) the temperature drops back to around 42F because the cold air from the Col. Basin is now making it over the pass (the previous day was much warmer) and continues to drop quickly going east; quicker than the car thermometer can keep up with.

9) Preceding east the temperature continues to generally drop, but with some warm spots and amazing variety.  This area was just below the inversion.

a) At Trillium Lake snopark a few miles east of Govt Pass the temperature was 34F when we first passed it.  When we came back 15 minutes later it was 27F.  When we'd got our gear on it was 33F.  When we returned it was 28F.

b) Preceding east from Trilliam Lake to Bennett Pass (near Hood Meadows ski area base) the temperature fluctuated wildly from 23F to 34F.  At two points we saw ice fog pouring like a waterfall over the road and surrounding terrain with fantastically rimed trees.  Bennett Pass at about 4700 ft was still within the cold pool with a temperature of 29F.

It seems that the fluctuations that we saw were a function of topography, elevation AND time.  Because of the closeness to the inversion layer, whenever a good wind gust came through warm air was ventilating into the cold layer.  The speed that the thermometer could respond was also an issue.

10) But the best part was after we were done snowshoeing and went for dinner at Timberline lodge.  We turned onto Timberline Road (elevation 3987 ft) and started the accent to Timberline.  Only a 1F change in the first 500 feet or so.  Then in 2.1 miles from about 4500 ft to 5200 ft the temperature went from 28F to 49F!!

At the Lodge around sunset it was in the mid-50's with a moderate north wind.  After dinner that wind had increased and the temperature was 51F. "